Wife got a will, 1 week before death of husband, how to challenge it

My father purchased property in Gandhinagar 2yrs ago and gave my brother POA to handle property on his behalf. My father lived in US and was remarried with a child. The original will does not include this property but one week prior to his death his wife changed the will which states this property is to be given to her. We were not advised of the new will as his wife had cut-off all communication with our father. The property is now fully constructed and is ready for handover and the wife's lawyer is claiming the property is hers. Can you please advise our rights? My brother and I reside in Australia but have OCI cards. My father resided in US and was an American Citizen. The wife is an American citizen.